Heat integration between processes: Integrated structure and MINLP model

Abstract

The previous method of integration [Kovač Kralj, A., Glavič, P., & Krajnc, M. (2002). Waste heat integration between processes. Applied Thermal Engineering, 22, 1259–1269] was extended to heat integration between processes using three possible steps: 1. internal integration of individual processes; 2. analysis of possible heat transfer between internally nonintegrated and integrated processes; 3. simultaneous external heat integration between the internally nonintegrated and the best internally integrated processes using the mixed integer nonlinear programming (MINLP). The method is based on energy saving. Simultaneous integration between processes can be performed using MINLP algorithm (step 3), in which alternatives suggested by pinch analysis of the heat transfer between several internally nonintegrated and integrated processes can be included (step 2). The fraction of the maximum integration between processes can be calculated. The integration between the processes can be carried out using all the three steps, or by the first and the third step or by the last step only, depending on the complexity of the problems. The method is very general, it can be used in new designs and in existing processes integration. The approach has been illustrated by integrating four existing complex processes using pinch analysis and MINLP. The objective was to maximize the annual profit of integration between processes and retrofits. The simultaneous MINLP integration of the four processes has selected only two retrofitted ones yielding total additional profit of 1.94 MUSD/a.